1. Technical Field
The present invention relates to a liquid-cooled heat sink and a manufacturing method thereof which is connected to a semiconductor device through a ceramic substrate, and discharges a coolant after the coolant has absorbed the heat emitted by the semiconductor device.
2. Description of the Related Art
As shown in FIGS. 5 and 6, a conventional example of this type of heat sink is a liquid-cooled heat sink 1 in which a flat bar formed from a malleable material made of aluminum or aluminum alloy is cut to a prescribed length, flat block 2 is fabricated by milling in which a meandering groove 2a is formed, cover 3 is fabricated by cutting a bar formed from a malleable material made of aluminum or aluminum alloy to a prescribed length, and this cover 3 is placed over the above flat block 2 so as to form passage 4 in which coolant passes through the above grooves 2a. 
The above liquid-cooled heat sink 1 has the problem of having an extremely large number of machining steps which increases the production cost.
In order to solve this problem, the present invention provides a liquid-cooled heat ink in which the above flat block and cover are formed by aluminum die casting. In this heat sink, since the grooves and so forth can be formed with good precision by cast extraction, the number of machining steps can be reduced considerably.
However, in contrast to the thermal conductivity of a malleable material made of aluminum or aluminum alloy being about 180 to 230 W/m.xc2x0 C., the thermal conductivity of the aluminum material for die casting (ADC12) in the above liquid-cooled heat sink formed by aluminum die casting of the prior art is about 50% of the above malleable material at about 92 W/m.xc2x0 C., thereby resulting in the problem of inferior heat radiation efficiency.
In addition, when a heat sink is fabricated by aluminum die casting, solidification and shrinkage causes cracks as well as voids depending on the shape of the heat sink, thereby resulting in the risk of leakage of coolant.
A first object of the present invention is to provide a liquid-cooled heat sink and a manufacturing method thereof that is able to obtain high thermal conductivity as well as satisfactory moldability and corrosion resistance by using a malleable material made of aluminum or aluminum alloy, while also being able to prevent leakage of coolant by preventing the occurrence of cracks and so forth.
A second object of the present invention is to provide a liquid-cooled heat sink and a manufacturing method thereof that is able to improve the heat radiation efficiency of the heat sink by increasing the amount of heat absorbed from the casing and fins by coolant passing through a passage as a result of increasing the contact surface area with the coolant, snaking the passage, or allowing heat to rapidly transfer to the fins from upper and lower walls of the casing.
A third object of the present invention is to provide a liquid-cooled heat sink and a manufacturing method thereof that is able to inhibit increases in production cost by forming through holes by extrusion molding to reduce the number of machining steps, or by unitarily forming the fins and covers with the casing in a single step.
As shown in FIG. 1, the invention as claimed in claim 1 is an improvement of a liquid-cooled heat sink having a passage 23 in which coolant is able to pass and which is joined to a ceramic substrate.
Its characteristic constitution is comprised of: a casing 12 of which both ends are open and in which a plurality of through holes 12a extending from one end to the other end are formed by a plurality of dividing walls 13-15, notches 16 formed in one or both ends of the plurality of dividing walls 13-15, a corrugated fin 17 inserted into each of the plurality of through holes 12a which demarcates each of the through holes 12a into a plurality of slots 12b extending from one end to the other end of casing 12, a pair of covers 18,19 that close both ends of casing 12, and an inlet 18a and outlet 18b of the coolant formed in casing 12 or covers 18,19; wherein, passage 23 is formed by communication of notches 16 and slots 12b, and inlet 18a and outlet 18b are composed so as to be positioned on both ends of passage 23.
In this liquid-cooled heat sink according to claim 1, since fin 17 is inserted into each through hole 12a, the contact surface area between heat sink 11 and coolant increases, thereby making it possible to improve the heat radiation efficiency of heat sink 11.
The invention as claimed in claim 2 is the invention as claimed in 1 wherein, as shown in FIG. 1, notches 16 are composed of first notches 16a formed in one end of very other plurality of dividing walls 13-15, and a second notch 16b formed in the other end of dividing wall 14 in which said first notches 16a are not formed, and passage 23 is composed so as to snake by communicating with said first notches 16a, second notch 16b and slots 12b. 
In this liquid-cooled heat sink according to claim 2, since passage 23 snakes, the amount of heat absorbed from casing 12 and fins 17 by coolant that passes through this passage 23 increases, thereby making it possible to improve the heat radiation efficiency of heat sink 11.
As shown in FIGS. 1 and 3, the invention as claimed in claim 3 is a production method of a liquid-cooled heat sink comprising: a step in which a casing 12, of which both ends are open and in which a plurality of through holes 12a extending from one end to the other end are formed by a plurality of dividing walls 13-15, is fabricated by extrusion molding of a malleable material made of aluminum or aluminum alloy, a step in which notches 16 are formed by milling in one or both ends of the plurality of dividing walls 13-15, a step in which each of the through holes 12a is demarcated into a plurality of slots 12b extending from one end to the other end of casing 12 by inserting a corrugated fin 17 into each of the plurality of through holes 12a, and a step in which a passage 23 is formed that is composed of notches 16 and slots 12b by closing both ends of casing 12 with a pair of covers 18,19.
In this production method of a liquid-cooled heat sink according to claim 3, since heat sink 11 is formed using a malleable material made of aluminum or aluminum alloy, a heat sink 11 can be obtained having high thermal conductivity as well as satisfactory moldability and corrosion resistance. In addition, since through holes 12a serving as passage 23 can be formed by extrusion molding, the number of machining steps can be reduced as compared with heat sinks of the prior art, thereby making it possible to inhibit increases in production costs.
As shown in FIGS. 1 and 3, the invention as claimed in claim 4 is the invention as claimed in claim 3 wherein, notches 16 are composed of first notches 16a formed by milling in one end of every other plurality of dividing walls 13-15, and a second notch 16b formed by milling in the other end of dividing wall 14 in which first notches 16a are not formed, and passage 23, which snakes by communicating with first notches 16a, second notch 16b and slots 12b, is formed by closing both ends of casing 12 with covers 18,19.
In this production method of a liquid-cooled heat sink according to claim 4, heat sink 11 of the above claim 2 can be fabricated by snaking passage 23 with only a slight increase in production cost.
As shown in FIGS. 1 through 3, the invention as claimed in claim 5 is the invention as claimed in claim 3 or 4 wherein, after forming fins 17 and covers 18,19 from a brazing sheet in which a 4000 series Alxe2x80x94Si alloy brazing material is coated by cladding onto the surface of a malleable material made of aluminum or aluminum alloy, and assembling fins 17 and covers 18,19 in casing 12, fins 17 and covers 18,19 are brazed with said 4000 series Alxe2x80x94Si alloy brazing material to casing 12 by holding for 0.1 to 1 hour at 570 to 620xc2x0 C. in a vacuum or inert gas atmosphere.
In this production method of a liquid-cooled heat sink according to claim 5, since fins 17 and covers 18,19 can be integrated with casing 12 in a single step, increases in the production cost of heat sink 11 can be suppressed.